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Quantum Physics

Title:
An anomaly of non-locality

Abstract: Ever since the work of Bell, it has been known that entangled quantum states
can rise non-local correlations. However, for almost forty years, it has been
assumed that the most non-local states would be the maximally entangled ones.
Surprisingly it is not the case: non-maximally entangled states are generally
more non-local than maximally entangled states for all the measures of
non-locality proposed to date: Bell inequalities, the Kullback-Leibler
distance, entanglement simulation with communication or with non-local boxes,
the detection loophole and efficiency of cryptography. In fact, one can even
find simple examples in low dimensions, confirming that it is not an artefact
of a specifically constructed Hilbert space or topology. This anomaly shows
that entanglement and non-locality are not only different concepts, but also
truly different resources. We review the present knowledge on this anomaly,
point out that Hardy's theorem has the same feature, and discuss the
perspectives opened by these discoveries.